Preheat the oven to 375°F (190°C).
In a large mixing bowl, combine the cooked chicken, marinara sauce, half of the mozzarella cheese, grated Parmesan cheese, minced garlic, oregano, basil, salt, and pepper. Mix well.
In another bowl, whisk the eggs until well combined. Add the almond flour and mix until you have a thick batter.
Spread half of the almond flour mixture evenly on the bottom of the greased casserole dish.
Pour the chicken mixture over the almond flour layer, spreading it out evenly.
Top with the remaining almond flour mixture, spreading it to cover the chicken layer.
Sprinkle the remaining mozzarella cheese on top.
Place the casserole in the preheated oven and bake for 30-35 minutes, or until the top is golden and bubbly.
Once done, remove from the oven and let it sit for 5-10 minutes before serving.
Garnish with fresh basil leaves, if desired.